4-chloro-2-fluoro-3-methoxyphenylboronic acid (PBA), and 2-(4-chloro-2-fluoro-3-methoxyphenyl)-1,3,2-dioxaborinane (PBE) are useful in the synthesis of 6-(poly-substituted aryl)-4-aminopyridine-2-carboxylates and 2-(poly-substituted aryl)-6-amino-4-pyrimidinecarboxylic acids, which are useful as herbicide intermediates.
PBA may be synthesized by reacting 2-chloro-6-fluoroanisole with n-butyl lithium and trimethyl borate B(OMe)3, adding an aqueous base to the reaction mixture, diluting the reaction mixture with acetonitrile, and acidifying the reaction mixture with hydrochloric acid. PBA may be esterified using 1,3-propanediol to form PBE.
It would be desirable to be able to reduce unit operations by isolating and using a precursor to either PBA or another 4-chloro-2-fluoro-3-substituted-phenylboronic acid to efficiently synthesize 6-(poly-substituted aryl)-4-aminopyridine-2-carboxylates and 2-(poly-substituted aryl)-6-amino-4-pyrimidinecarboxylic acids.